The aim of this study was to develop a laboratory animal model in New Zealand White (NZW) rabbits, Oryctolagus cuniculus, to establish a three-dimensional grafting environment for horizontal and vertical bone regeneration using osseous shell technique, as done in human patients. Laboratory animals commonly used employed in biomaterial bone studies include small animals mice, rats, hamsters, guinea pigs, and rabbits as well as large animal such as goats, dogs, and primates. [37–39] Rodent models have inherent limitations when compared to larger models. Rodents have smaller long-bones, more fragile cortex, and do not show Haversian-type remodeling in the cortex.  Rabbits are the largest species in the small animal category, so they are least susceptible to the complex and stringent extra clearance processes that central ethics committees normally impose. They are non-aggressive, are easy to examine, have a faster vital ability to mature and bread, and can be locally bred. [17, 37–39] The histology of rabbit bone differs from that of people, consisting of thick Haversian bone and layers of vascular-longitudinal canals. [37–39] Nonetheless, similarities in human and rabbit bone mineral density and hardness have been shown in previous publications. [38–40] Rabbits in contrast to rodents have accelerated skeletal metabolism and enhanced bone turnover (primarily cortical remodeling). [37–39] The rabbit model is useful for bone augmentation experiments because the animal replicable, convenient to house and anaesthetised, can provide large surgical fields for conducting technical procedures, and can withstand the trauma of surgery. [38, 39]
Autogenous bone grafts are often regarded as the gold standard in augmentative surgical procedures, particularly vertical augmentations. [4–6, 41, 42] The major issues reported in the literature about autogenous full block transplants include the resorption rates ranging from 21–25% as well as limited supply. [10, 41, 43]. Khoury described the shell technique to avoid these issues. [10, 11, 41] The shell approach makes effective use of bone block, allowing for considerably bigger bone volume to be supplemented with the same harvesting volume, while on the other hand, resorption rates are decreased to 5–9 percent by adhering to basics of wound healing principles. [41, 44, 45] Vertical bone augmentations and the shell approach, in particular, are advanced technique procedures that need advanced surgical skills and technical preparation to obtain desired results. [41, 44–48]
In modern clinical practice, many bone grafting materials and membrane techniques, with or without bone morphogenetic proteins, transforming growth factors, platelet-derived growth factor, and basic fibroblast growth factors, have also been reported to regenerate bone efficiently. With the current usage of human allogeneic bone cortices, further intraoral or extraoral bone block harvesting can indeed be skipped, minimising the total risk of problems and patient morbidity while providing clinical outcomes equivalent to autogenous bone shells. [41, 50, 51] Several clinical report indicated favorable outcomes with human allogeneic bone blocks for bone grafting procedures conducted according to the osseous shell technique. [41, 50] While there is little evidence on the use of xenogenic and allogeneic particulate bone material and blocks in various forms, there is much less on the use of allogeneic cortical plates for the shell approach. In initially disclosed case reports, the integration of human allogeneic bone plates and autogenous bone chips seems to be a viable substitute to autogenous implants in complex bone augmentation procedures; that being said, these researches were often case-controlled cohorts with no proper comparative studies published in credible animal models for in-depth preclinical evaluation. [41, 50, 52] Several studies have reported the reduction bone resorption rate and modulation of bone turnover and formation by using barrier membranes over augmented bone blocks.  [45, 54] These adjunctive interventions prompt us more towards developing a reliable animal model to provide a solid biological basis for furher in-vivo testing of bone grafting techniques to optimize the clinical outcome.
Within the limitation of the study, the present animal models provided a suitable environment for the testing of the osseous shell technique as seen by the excellent clinical handling of the material and ease of approach. Therefore, the rabbit model seems to represent a safe environment for regulated three-dimensional bone augmentation. However, its clinical applicability may be more challenging in complicated defect patterns, necessitating more research.